CHAPTER VII. 



THE STERNUM. 



THE Sternum of Mammals is a bone, or generally a series 

 of bones, placed longitudinally in the middle line, on the 

 inferior or ventral aspect of the thorax, and connected on 

 each side with the vertebral column by a series of more or 

 less ossified bars called ribs. 1 



It is present in all Mammals, but varies much in character 

 in the different groups. 



When in its usual and most complete form (see Fig. 31), 

 it may be divided into three parts, called respectively- 



1. Presternum, or " manubrium sterni " of human ana- 

 tomy. 



2. Mesosternum, body of the sternum or gladiolus. 



3. Xiphisternum, xiphoid or ensiform process of the ster- 

 num. 



The mesosternum is usually composed of several distinct 

 segments, which may become ankylosed together, but more 

 often permanently retain their individuality, being con- 

 nected either by fibrous tissue or by synovial joints. 



1 For much valuable information upon the structure and development 

 of the sternum, see W. K. Parker's " Monograph on the Shoulder-girdle 

 and Sternum of the Vertebrata," published by the Ray Society, 1868. 



